CODEWITHSUNDEEP
javaarrays
sebastian-thomas
sebastian-thomas

Reputation: 25

create an array of class instances in java

I am pretty new to java.

I want to have an array of a class whose length may vary during run time

code:

class Num
{
  ......
  ......
}

if Num is my class , how will i create new instances. My current code is pretty similar to:

Num n[ ];
int length=0;
.
.
.
n[length++]=new Num();

from this code I'm getting error :

"Uncompilable source code - variable factors might not have been initialized"

Upvotes: 3

Views: 8178

Answers (4)

Heshan
Heshan

Reputation: 1

The simple way to do this is by using ArrayList

ArrayList<Num> numList = new ArrayList<>();
    // Add elements to the ArrayList
    numList.add(new Num());
    numList.add(new Num());

Upvotes: 0

Kumar Vivek Mitra
Kumar Vivek Mitra

Reputation: 33544

Use the Java Collection

List will be good if sequence is more important.

Set if uniqueness is important

Map when key-value pair is important

List<MyClass> arrList = new ArrayList<MyClass>();

arrList.add(mobj1);
arrList.add(mobj2);
arrList.add(mobj3);

for(MyClass m : arrList){

      // m is the Values of arrList stored in

 }

Upvotes: 2

Kazekage Gaara
Kazekage Gaara

Reputation: 15052

You can use an ArrayList for this purpose.

ArrayList<Num> myListOfNum = new ArrayList<Num>();

and then keep adding the objects of Num as and when required.

Num num1 = new Num();
myListOfNum.add(num1);
Num num2 = new Num();
myListOfNum.add(num2);

EDIT:

And to access you can use the get() method along with the specific index.

Num tempNum = myListOfNum.get(indexGoesHere);

Upvotes: 7

amit
amit

Reputation: 178521

You need to first create the array itself, before you are trying to set the elements in it.

 Num[] n = new Num[SIZE];

Note that Num n[]; is just declaring a variable of type Num[] with the identifier n.

Note however, that in java - arrays are of fixed lengths. If you are looking for a variable length array, an array is probably not what you need. @KazekageGaara suggested an alternative - for this purpose.

Upvotes: 3

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